A liquid crystal display device is now being widely used attributed to its characteristics such as slim profile, light weight, and low electrical power consumption. The liquid crystal display device includes a pair of substrates and a liquid crystal layer interposed therebetween. Further, the liquid crystal device provides display by controlling an alignment direction of liquid crystal molecules contained in the liquid crystal layer by appropriately applying a voltage to electrodes arranged on liquid crystal layer side-surfaces of the substrates. The liquid crystal display device usually includes a liquid crystal alignment film (hereinafter, simply referred to as “alignment film”) for controlling the alignment direction of the liquid crystal molecules, and the alignment film is arranged on the liquid crystal layer side-surface of the substrate.
As a material for such an alignment film constituting the liquid crystal display device, resins such as polyamic acids, polyimides, polyamides, and polyesters are conventionally used. Among them, polyimides have been much used for liquid crystal display devices attributed to its excellent physical properties such as heat resistance, affinity with liquid crystals, and mechanical strength compared with other organic resins.
Methods for printing an alignment film include spin coat method, roll coat method, flexographic printing, and inkjet printing. Flexographic printing has been suitably used for pattern printing. In this method, ink is put on an APR plate uniformly and is transferred to a substrate. This method is less likely to cause film thickness irregularity. However, from the standpoint of achieving high throughput, inkjet printing is suitable for printing the film on a large substrate of the sixth or higher generation.
The technical art about formation of an alignment film by inkjet printing is disclosed against this background. More specifically, a composition for forming a liquid crystal alignment film is disclosed which comprises: a solvent containing 10% by weight or more of an amide compound; and a material for forming a liquid crystal alignment film dissolved in the solvent (for example, refer to Patent Document 1). Moreover, a vacuum freeze-drying method is disclosed which comprises the steps of applying a polyimide alignment film on a substrate by inkjet application, and cooling the substrate to freeze the medium, instead of heating the substrate to dry the medium, so that the medium sublimes in vacuo (for example, refer to Patent Document 2). Furthermore, a thin-film forming apparatus is disclosed which comprises: a vacuum chamber as a room for forming a film by spraying application, which includes at least a substrate transfer table, an inkjet head, and a head supporting member therein; and decompressing means for decompressing the vacuum chamber in order to perform film formation by spraying application in vacuo (for example, refer to Patent Document 3).
Moreover, a protective and alignment film for liquid crystals is disclosed which has excellent physical properties including heat resistance, chemical resistance, adhesion with a glass substrate and color filter, transparency, and printability, and is excellent in alignment property and planarizing performance. Specifically, a protective and alignment film for liquid crystals is disclosed which comprises a polyimide film formed by heating to dry a liquid film comprising a resin composition containing a polyamide acid that has the weight average molecular weight of 1000 to 20000, the liquid film being formed on the surface of a liquid crystal holding substrate by a printing method, and the surface having an electrode formed thereon (for example, refer to Patent Document 4).
Furthermore, a substrate with an alignment film for liquid crystal elements is disclosed as a technical art related to a photo-alignment film. Specifically, the substrate with an alignment film for liquid crystal elements is disclosed which comprises a polyimide coating formed on the substrate, the polyimide coating being prepared by polymerizing a layer comprising a composition for forming an alignment film which contains polyimide or a polyimide precursor. The polymerization includes sequential polymerization in a direction corresponding to the direction of a polarization axis of the irradiated light and polymerization by linear polarized light (for example, refer to Patent Documents 5).
In addition, a composition for photo-aligned liquid crystal alignment film is disclosed which comprises a recurring unit represented by a general formula (I):
(in the formula (I), X representing a tetravalent organic group and Y representing a divalent organic group). Further, the composition comprises polyimide or a precursor thereof which has a divalent organic group represented by a general formula (II):
(in the formula (II), R2, R3, and R4 being each independently selected from —H, —CH3, and —CH2CH3) as at least a part of Y (for example, refer to Patent Document 6).    [Patent Document 1]    Japanese Kokai Publication No. 2006-53380    [Patent Document 2]    Japanese Kokai Publication No. 2006-281189    [Patent Document 3]    Japanese Kokai Publication No. 2006-289355    [Patent Document 4]    Japanese Kokai Publication No. Hei-11-95227    [Patent Document 5]    Japanese Kokai Publication No. Hei-07-72483    [Patent Document 6]    Japanese Kokai Publication No. 2001-40209